KINEMATICS OF LOW-STRAIN FAULTS ASSOCIATED WITH THE EASTERN TERMINUS OF THE CADY FAULT, EASTERN CALIFORNIA SHEAR ZONE

Faults with wide-ranging orientations, kinematics, and cumulative slip are part of the right-lateral shear associated with the Eastern California Shear Zone (ECSZ). To better constrain the temporal and spatial variations in the kinematics of ECSZ deformation, I mapped bedrock and surficial geology in the tectonic accommodation zone east of the termination of the Cady Fault (CF). The east-striking sinistral CF is the southern boundary of the northeastern Mojave domain, a sinistral network of E-NE-striking faults separating primarily NW-striking dextral faults of the ECSZ. Furthermore, at its eastern terminus the CF branches into the east-vergent, west-dipping, N-NE striking Elephant Seal thrust fault (ESF). East of the ESF and towards the topographic low occupied by Broadwell Lake, moderate-relief Pliocene(?) fanglomerate composed of plutonic and Miocene volcanic clasts are juxtaposed against mountains composed of Mesozoic(?) gneissic and dioritic bedrock by a near vertical fault. This north-striking fault expresses oblique, dextral strike-slip kinematics consistent with up-to-west exhumation of the fanglomerate. Parallel to, and < 1 km to the east of this fault contact, within bedrock mountains, are numerous steeply dipping, north-striking dextral faults. Fault-core cataclasites appear immature, retaining coarse-grained, gravel-sized angular fragments of neighboring source bedrock. These fault cores also locally contain meter-wide zones of highly sheared, mechanically weak rock revealing remnant parent material texture and fabric. Additionally, these north-striking faults crosscut, and hence must post-date, east-striking faults with better developed fault-core material. The geometry of these faults is similar to surface ruptures during the 1992 Landers and 1999 Hector Mine earthquakes, which revealed broad northwesterly dextral deformation, parallel to the overall strain of the ECSZ, connected by shorter, north-striking transfer faults. These secondary, north-striking, and apparently youthful faults may transfer strain among nearby thrust faults or northwest-striking, dextral faults, such as the Ludlow fault. The presence of this seemingly low-strain, north-striking system may represent a more recent change in the ECSZ stress field in this area.